This invention relates to the field of medical testing and, more particularly, to a method and apparatus for measuring human glucose levels.
For a number of years, polarographic systems with an enzyme electrode have been used to measure glucose level in blood samples. For example, Clark Patent 3,539,455 teaches the use of a platinum anode and silver cathode to measure the hydrogen peroxide produced by the reaction of glucose and oxygen in the presence of a glucose oxidase enzyme. Newman Patent 3,979,274 discloses a laminated membrane for an enzyme electrode in which the enzyme is coupled with an adhesive between the lamina. The lamina of the multi-ply membrane comprise an outer support layer that serves as a barrier to high molecular weight substances and an inner homogeneous layer that serves as a barrier to interfering low molecular weight materials, but permits hydrogen peroxide to pass through, and an intermediate enzyme layer that reacts with glucose and bonds the outer and inner layers together. Glucose passes through the outer layer and reacts with a surplus of oxygen in the presence of the contained enzyme. Hydrogen peroxide, which is one of the reaction products, passes through the inner layer to the electrode. The resulting electric current is a measure of the level of glucose in the sample fluid under test.
Reinhart Patent 4,750,496 teaches the use of the described polarographic cell system to measure the glucose level (concentration) on a mucosal surface in the oral cavity of a living being. Specifically, the enzyme electrode membrane of a glucose monitoring instrument is positioned on the buccal mucosa, and a surplus of oxygen from the atmosphere is conveyed to the membrane through a passageway in the instrument. The oxygen reacts with the glucose that migrates through the outer layer of the membrane in the present of the enzyme, and the resulting hydrogen peroxide migrates through the inner layer of the membrane to the electrodes while the membrane remains in contact with the mucosal surface. Thus, a noninvasive glucose measurement is made on a sample of mucosal fluid of patient in situ, rather than carrying a blood fluid sample to a free standing instrument.